Depends on what you're doing
1) For gaming it won't be that much of an improvement in general. If you're doing a lot of media encoding or other thread heaving work then you will notice the improvement. If it's mainly just for gaming though you are better off upgrading your cooling solution and overclocking, like say with a Corsair H100
2) If you're currently doing things that are using all 8GB then you will notice an improvement, but if you aren't then not so much. If you only have 1 8 GB stick of Corsair as your sig suggests then just get another one with the same timings to run in dual channel.
3) Yes but it's easy to run out of space. You can install a window OS on 32GB, but you will constantly need to watch the space you have. Some programs don't assume you have more than one drive when they try to install. Sure most modern games give you the option, but a few games and programs don't and you'll notice it if you only have a 32GB boot drive. Get at least a decent 120 GB drive. It will be more useful to you at this point